1) Field of the Invention
The present invention relates to a radio-controlled timepiece that automatically performs the Daylight Saving Time (DST) to standard time (ST), or vice versa, adjustment.
2) Description of the Related Art
In the countries such as the United States, Japan, Germany, and the United Kingdom, time information is transmitted on a carrier wave of a long-wave standard-frequency (hereinafter, “standard frequency”), i.e. a frequency of several tens of kilohertzs. The radio-controlled timepieces that receive the standard frequency and adjust the time have nowadays become common.
The radio-controlled timepiece receives the standard frequency at predetermined time intervals, and clocks time based on a standard signal until the reception of the standard frequency is performed next time. An internal oscillator circuit and an internal frequency divider circuit generates the standard signal from the standard frequency. The standard frequency includes information on a current time, DST, and leap year, so that the radio-controlled timepiece can display the exact current time, date, and day of the week only from the information included in the standard frequency.
However, some typical problems occur when using the radio-controlled timepieces in the United States. Because in the United States the standard frequency does not include information about when to switch to DST or when to switch to ST, there are four time regions, and the standard frequency includes information about Coordinated Universal Time (UTC), it is not possible to adjust to an appropriate time.
Furthermore, in the United States, when to switch to DST or to ST becomes clear only on the UTC day (i.e., UTC 0 o'clock to 24 o'clock) of performing the switching, sometimes a correct timing of the switching can not be obtained depending on when the standard frequency is received. Especially when UTC is still some time on the previous day in comparison with the local time in each time region as shown in FIGS. 3 and 4, then the switching is performed erroneously.